1. Field of the Invention
The present invention relates to an electrical drive-in tool for driving in fastening elements and including a driving ram displaceable in a guide for driving in a fastening element, at least one drive flywheel for driving the driving ram, and a drive unit for driving the at least one drive flywheel and including an electric motor for rotating the at least one drive flywheel, and a drive coupling for connecting a coupling section of the driving ram with the at least one drive flywheel.
2. Description of the Prior Art
In electrical drive-in tools of the type described above, the driving ram is accelerated by the flywheel that is driven by a motor. In drive-in tools, the drive-in energy, which is supplied by an accumulator, amounts maximum to about 35-40 J. In drive-in tools, which were developed on the basis of a flywheel principle, the energy which is stored in the flywheel, must be transferred to the driving shaft by a coupling. The coupling should be capable of being very rapidly actuated and should be capable of transmitting a very high power in a short period of time. The coupling also should be capable of being rapidly deactuated at the end of the drive-in process.
A drive-in tool of the type described above is disclosed in U.S. Pat. No. 4,928,868. In the drive-in tool of U.S. Pat. No. 4,928,868, the driving ram is displaced between a motor-driven flywheel and an idler wheel. In order to frictionally couple the driving ram with the flywheel, the driving ram is displaced toward the flywheel by an adjusting mechanism, is pressed against the circumferential surface of the flywheel, and is accelerated.
A drawback of the known drive-in tool consists in that upon coupling of the driving ram with the drive flywheel slippage occurs when the quasi-stationary driving ram contacts the rotating flywheel. The slippage leads, on one hand, to energy losses and, on the other hand, to wear of the contact surfaces. The slippage also causes a time delay in the acceleration of the driving ram during braking of the flywheel. Therefore, obtaining of high rotational speeds of the flywheel and, thereby, of a drive-in energy of more than 35 J is not possible. This is because the resulting increased heating caused by friction leads to damage of the driving ram and of the surface of the flywheel, which further increases wear of these parts.
Accordingly, an object of the present invention is a drive-in tool of the type discussed above in which a high drive-in energy can be obtained in a technically simple way, and the above-mentioned drawbacks of the known drive-in tool are eliminated.